1. Field of the Invention
This invention relates to a pressure sensor which converts fluid pressures into electric signals, and more particularly to a pressure sensor which detects fluid pressures by means of a diaphragm and converts distortions of the diaphragm into electric signals.
2. Prior art of the Invention
This type pressure sensor generally detects changes in fluid pressure by means of distortions of diaphragm and generates output powers by means of a strain gauge attached to the diaphragm. In such pressure sensor, a metal resistance wire such as nickel-copper system, or a semiconductor of a piezo-resistance form or a diffusion form has been used as strain gauge. In the strain gauge of the metal resistance wire where the stability in temperatures will be high, however, there are some drawbacks that the output voltage will be small, for example under 8 mV, that the maximum using temperature will be low, for example order of 80.degree. C., and that the metal resistance wire will be apt to be destroyed due to the excess distortion because the maximum anti-tension is small. In the strain gauge of the semiconductor where the sensibility, namely, the rate of the gauge will be high, however, there are some drawbacks that the stability in temperatures will be low, for example above 0.1% FS/.degree.C., where FS represents full scale, that the maximum using temperature will be low, for example 100.degree. C., and that a countermeasure for protecting the semiconductor should be necessary because the semiconductor is weak in an impulsive force. Accordingly, the application scope of the gauge will be much limited due to the above characteristics of the strain gauge.